Systems and methods for performing blood processing and/or fluid exchange procedures

ABSTRACT

A flow management system for extracorporeal blood treatment application helps to ensure proper balance of incoming and outgoing fluids by precise balancing of relatively small balance chambers. The invention employs combinations of features that help to ensure accuracy including underfilling of the waste flow side of a fixed volume chamber and mechanical connections to synchronize valves and pumps.

This is a continuation-in-part of U.S. application Ser. No. 09/451,238,filed Nov. 29, 1999, now abandoned, Ser. No. 09/513,773, filed Feb. 25,2000, issued as U.S. Pat. No. 6,579,253, Ser. No. 09/513,911, filed Feb.25, 2000, issued as U.S. Pat. No. 6,638,478, Ser. No. 09/513,771, filedFeb. 25, 2000, issued as U.S. Pat. No. 6,673,314, Ser. No. 09/513,446,filed Feb. 25, 2000, now abandoned, Ser. No. 09/513,902, filed Feb. 25,2000, issued as U.S. Pat. No. 6,554,789, Ser. No. 09/512,927, filed Feb.25, 2000, issued as U.S. Pat. No. 6,589,482, Ser. No. 09/512,929, filedFeb. 25, 2000, issued as U.S. Pat. No. 6,638,477, Ser. No. 09/513,910,filed Feb. 25, 2000, issued as U.S. Pat. No. 6,830,553, Ser. No.09/513,564, filed Feb. 25, 2000, now abandoned, Ser. No. 09/513,915,filed Feb. 25, 2000, now issued as U.S. Pat. No. 6,595,943, and Ser. No.09/894,236, filed Jun. 27, 2001, now U.S. Pat. No. 6,686,946, which is adivisional of Ser. No. 08/800,881, filed Feb. 14, 1997, now abandoned.Each of the above-identified applications is expressly incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to systems and methods for processing blood orother fluids that are conveyed to and from an animal body, e.g., fordialysis, filtration, pheresis, or other diagnostic or therapeuticpurposes. The systems may include roller guides on pumps, alignmentusing pump tubing fitments, air detector tube pushers for loading, bloodleak detector, temperature sensing, and pressure sensing.

BACKGROUND OF THE INVENTION

There are many types of blood processing and fluid exchange procedures,each providing different therapeutic effects and demanding differentprocessing criteria. Typically, such procedures entail the removal ofblood or another fluid from an individual and the return of blood oranother fluid to the individual in a controlled fashion. Examples ofsuch procedures include hemofiltration (HF), hemodialysis (HD),hemodialysis with hemofiltration (HDF), and peritoneal dialysis (PD).

In carrying out these procedures, specially designed fluid circuits,which can be complex and convoluted, are placed into a prescribedoperative association with pumps, clamps, and sensors, which aretypically mounted on a machine that is also specially designed to carryout the intended procedure. Numerous safety and control elements of thefluid circuit and the machine must be placed in operative association inorder to carry out the procedure in the intended way. As a consequence,the process of loading a fluid circuit on the machine can be tedious anderror-prone.

There is a need for simplicity and convenience when loading a fluidcircuit in a prescribed way in association with safety and controlelements on a blood and/or fluid processing machine.

Typically, when performing the blood processing and fluid exchangeprocedures of the type just described, a replacement or make-up fluid isreturned back to the individual in some proportion to the amount offluid that is removed from the individual. The type and make-up offluids that these procedures handle vary according to the particulartreatment modality being performed, e.g., among waste fluid andreplacement fluid (in HF or HDF); or replacement fluid and dialysissolution (in HD or HDF); or fresh peritoneal dialysis solution and spentperitoneal dialysis solution (in PD. Controlled balancing of fluidamounts can be achieved by monitoring the weights of fluid removed andreplacement or makeup fluid. However, weight sensing itself requiresadditional fluid circuit elements (e.g., weigh containers), additionalhardware elements (e.g., weigh scales), as well as additional processingcontrol and feedback features. These items add further complexity to thesystems and their operation.

There is also a need for simplicity and convenience when undertaking acontrolled balancing of fluids during a blood processing and/or fluidexchange procedure.

SUMMARY OF THE INVENTION

One aspect of the invention provides systems and methods for processingblood and/or other fluids, which include a fluid interface between afluid processing circuit and a fluid processing machine that makespossible a fast, convenient, one step process for loading the fluidprocessing circuit on the machine.

In one embodiment, the systems and methods consolidate all blood andfluid flow paths in a unitary, easily installed cartridge. The cartridgeestablishes a fixed orientation for fluid circuit elements and theiroperative interface with the hardware elements, such as pumps, sensors,and clamps, on the processing machine. The fixed orientation requiresthat all safety and control elements on the cartridge and machine arebrought into operative association in a single, straightforward loadingstep. Due to the cartridge, the operator cannot place one part of thefluid circuit into an operating condition with one or more hardwareelements on the machine without placing the entire fluid circuit into anoperating condition with all the hardware elements on the machine. Theconsolidation of all blood and fluid flow paths in a single, easilyinstalled cartridge also avoids the potential of contamination, byminimizing the number of connections and disconnections needed during agiven treatment session.

Another aspect of the invention provides systems and methods forprocessing blood and/or other fluids that makes possible the performanceof accurate, synchronized volumetric fluid balancing, without the needfor weight sensing.

Other features and advantages of the inventions are set forth in thefollowing specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a system that includes a machine andfluid processing cartridge that, in use, is mounted on the machine forconducting various types of blood processing and/or fluid exchangeprocedures;

FIG. 2 is a front perspective view of an embodiment of a machine thatcan form a part of the system shown in FIG. 1;

FIG. 3 is a plane view of the exterior surface of an embodiment of afluid processing cartridge that can form part of the system shown inFIG. 1;

FIGS. 4 to 6 are side elevation views showing the loading of the fluidprocessing cartridge shown in FIG. 3 onto the machine shown in FIG. 2;

FIG. 7 is a perspective exploded view of the fluid processing cartridgeshown in FIG. 3;

FIG. 8 is a plane view of the exterior surface of the fluid processingcartridge shown in FIG. 3, with the cover member removed to show thechannels that guide the passage of flexible tubing that forms a part ofthe fluid circuit carried by the cartridge;

FIG. 9 is a plane view of the interior surface of the fluid processingcartridge shown in FIG. 3;

FIGS. 10 and 11 are plane view of fluid management modules that form apart of the fluid circuit carried by the cartridge;

FIG. 12 is a schematic view of a fluid circuit for carrying outhemofiltration, which the cartridge shown in FIG. 3 can be configured toform;

FIG. 13 is a perspective view of the inside of the door of the machineshown in FIG. 2;

FIG. 14 is a largely schematic side section view of the overlaying fluidbalancing compartments that are part of the fluid management modulesshown in FIGS. 10 and 11, showing their orientation with valve elementscarried by on the machine shown in FIG. 2;

FIG. 15 is a front perspective view of an embodiment of a chassis panelthat the machine shown in FIG. 2 can incorporate;

FIG. 16 is a back perspective view of the chassis panel shown in FIG.15, showing the mechanical linkage of motors, pumps, and valve elementscarried by the chassis panel;

FIG. 17 is a side section view of one of the clamp elements shown inFIGS. 15 and 16;

FIG. 18 is a diagrammatic view of a telemetry network that can form apart of the system shown in FIG. 1; and

FIG. 19 is a plane view of a graphical user interface that the machineshown in FIG. 2 can incorporate.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. System Overview

FIG. 1 shows a system 10 that is well suited for handling fluids insupport of various types of blood processing and/or fluid exchangeprocedures. The system 10 includes a durable hardware component ormachine 16 (see FIG. 2) and a removable fluid processing cartridge 18(see FIG. 3) that is intended to be installed in operative associationwith the machine 16 for use (see FIGS. 4 to 6).

The system 10 is suitable for use in many diverse treatment modalitiesduring which blood and/or fluid are conveyed to and from an animal body.In particular, the system 10 is well suited for treatment modalitiesduring which one fluid is removed from the body and replaced withanother fluid in a controlled fashion. Such modalities include, e.g.,hemofiltration (HF), hemodialysis (HD), hemodialysis with hemofiltration(HDF), and peritoneal dialysis (PD).

For example, the system 10 can perform hemofiltration, e.g., to treat anindividual whose renal function is impaired or lacking, according todifferent selected protocols. The system 10 can be adapted to performhemofiltration at relatively high blood flow rates to enable relativelyshort session time intervals, as well as at lower blood flow rates andover longer session time intervals. The former protocol can be adoptedto achieve hemofiltration three or more times a week. The latterprotocol can be adapted to achieve an overnight treatment regime, whichcan be called “nightly hemofiltration.” Nightly hemofiltration can beconducted at intervals less or more frequent than three times a week.Alternatively, the system 10 can be adapted to perform hemofiltration onan acute basis, or on an intermittent chronic basis, at virtually anyprescribed time interval and treatment pattern that achieves themaintenance of uremic toxin levels within a comfortable range. Thus, thesystem 10 can be adapted to perform multiple hemofiltration treatmentsper day at varying session times, morning, afternoon, or night, or acombination thereof.

The system 10 can also just as readily be adapted to performhemodialysis (HD) or hemodialysis with hemofiltration (HDF). The fluidbalancing functions that the system 10 can perform, as will be describedin greater detail later, can also be readily adapted for use, eitherindividually or in combination, in systems intended to performprescribed peritoneal dialysis modalities.

The type and make-up of fluids that the system 10 can balance can andwill vary according to the particular treatment modality beingperformed, e.g., among waste fluid and replacement fluid (in HF or HDF);or replacement fluid and dialysis solution (in HD or HDF); or freshperitoneal dialysis solution and spent peritoneal dialysis solution (inPD). The terminology employed in this Specification in characterizing aparticular type or make-up of fluid, or as ascribing a source,destination, or direction of fluid flow in the context of describing onetreatment modality is not intended to be interpreted as being limited tothat particular type or make up of fluid or that particular flow source,destination, or direction. Rather, a person of skill in the art willreadily appreciate that the fluid type and make up and the flowparticulars relating to volumetric fluid balancing can vary withdifferent treatment modalities.

A. Fluid Processing Machine

The machine 16 (see FIG. 2) is preferably lightweight and portable,presenting a compact footprint, suited for operation on a table top orother relatively small surface normally found, e.g., in a hospital roomor in a home. The compact size of the machine 16 also makes it wellsuited for shipment to a remote service depot for maintenance andrepair.

Desirably, the machine 16 includes an operator interface 44 (see FIG.2). FIG. 19 shows a representative display 324 for the operatorinterface 44 for the machine. The display 324 comprises a graphical userinterface (GUI), which, in the illustrated embodiment, is displayed bythe interface 44 on the exterior of the door 28, as depicted in FIG. 2.The GUI can be realized, e.g., as a membrane switch panel, using anicon-based touch button membrane. The GUI can also be realized as a “C”language program.

The GUI 324 presents to the operator a simplified information input andoutput platform, with graphical icons, push buttons, and display bars.The icons, push buttons, and display bars are preferably back-lighted ina purposeful sequence to intuitively lead the operator through set up,execution, and completion of a given treatment session.

B. The Fluid Processing Cartridge

The processing cartridge 18 (see FIG. 3) provides the fluid interfacefor the machine 16. The fluid interface between the cartridge 18 andmachine 16 makes possible a fast and convenient one step process forloading the cartridge 18 for use on the machine 16 (see FIGS. 4 to 6).

In one embodiment, the cartridge 18 establishes a fixed orientation forfluid circuit elements and their operative interface with the hardwareelements, such as pumps, sensors, and clamps, on the machine 16. Thefixed orientation requires that all safety and control elements on thecartridge 18 and machine 16 are brought into operative association in asingle, straightforward loading step. Due to the cartridge 18, theoperator cannot place one part of the fluid circuit into an operatingcondition with one or more hardware elements on the machine 16 withoutplacing the entire fluid circuit into an operating condition with allthe hardware elements, including safety systems, on the machine 16.

Desirably, the cartridge 18 makes possible the elimination of air-bloodinterfaces, and/or positive pressure monitoring. In association with themachine 16, the fluid cartridge 18 can also perform accurate,synchronized volumetric fluid balancing, without the need for weightsensing, as will be described in greater detail later.

The consolidation of all blood and fluid flow paths in a single, easilyinstalled cartridge 18 avoids the potential of contamination, byminimizing the number of connections and disconnections needed during agiven treatment session. By enabling a dwell or wait mode on the machine16, the cartridge 18 can remain mounted to the machine 16 after onetreatment session for an extended dwell or break period and allowreconnection and continued use by the same person in a subsequentsession for any reason, for example, or in a continuation of a sessionfollowing x-rays or testing.

The cartridge 18 can therefore provide multiple intermittent treatmentsessions during a prescribed time period, without exchange of thecartridge 18 after each treatment session. The time of use confines aretypically prescribed by the attending physician or technical staff forthe treatment center to avoid bio-contamination and can range, e.g.,from 48 hours to 120 hours, and more typically 72 to 80 hours. Thecartridge 18 can carry a bacteriostatic agent that can be returned tothe patient (e.g., an anticoagulant, saline, ringers lactate, oralcohol) and/or be refrigerated during storage.

The single step loading function can be accomplished in various ways. Inthe illustrated embodiment (see FIG. 2), the machine 16 includes achassis panel 26 and a panel door 28. The door 28 moves on a pair ofrails 31 in a path toward and away from the chassis panel 26 (as shownby arrows in FIG. 2). A slot 27 is formed between the chassis panel 26and the door 28. As FIGS. 4 to 6 show, when the door 28 is positionedaway from the panel 26, the operator can, in a simple vertical (i.e.,downward) motion (see FIG. 4), move a fluid processing cartridge 18 intothe slot 27 and, in a simple horizontal (i.e., sideway) motion (see FIG.5), fit the cartridge 18 onto the chassis panel 26. When properlyoriented, the fluid processing cartridge 18 may rest on the rails 31 tohelp position the cartridge 18. As FIG. 6 shows, movement of the door 28toward the panel 26 engages and further supports the cartridge 18 foruse on the panel 26. This position of the door 28 will be called theclosed position.

The machine 16 preferably includes a latching mechanism 30 and a sensor32 (see FIG. 2) to secure the door 28 and cartridge 18 against movementbefore enabling circulation of fluid through the cartridge 18.

The cartridge 18 can be constructed in various ways. FIG. 3 (in anassembled view) and FIG. 7(in an exploded view) show an embodiment of acartridge 18, which can be used to in association with the machine 16 toperform a selected treatment modality. In this embodiment, the cartridge18 includes a preformed support frame 400 manufactured, e.g., bythermoforming polystyrene or another comparable material. The supportframe 400 presents an exterior surface 402 (shown in plane view FIG. 8)and an oppositely facing interior surface 404 (shown in plane view inFIG. 9).

When installed for use on the machine 16, the exterior surface 402 isoriented toward the door 28, and the interior surface 404 is orientedtoward the chassis panel 26. An icon 440 imprinted on the exteriorsurface 402 (see FIG. 8) guides the operator in mounting the frame 400on the chassis panel 26 in the proper front-to-back and up-and-downorientation.

As FIG. 7 best shows, the interior surface 404 of the frame 400 carriesa flexible fluid circuit 408. In the illustrated embodiment, theflexible fluid circuit 408 comprises one or more individual fluidmanagement modules. The modules can be dedicated to different processingfunctions. For example, one module can handle fluid being removed fromthe body, while another module can handle fluid being supplied to thebody. These processing functions can be synchronized by various means oforienting the modules with each other, and with the common hardwareelements on the machine 16.

In the illustrated embodiment (see FIG. 7), two modules 424 and 426 areprovided, which are shown individually in FIGS. 10 and 11, respectively.As FIG. 7 shows, lengths of flexible tubing 418 communicate with modules424 and 426 of the flexible fluid circuit 408, to convey fluid to andfrom the modules 424 and 426. Together, the flexible fluid circuit 408and tubing 418 form a fluid processing circuit 420.

The modules 424 and 426 themselves can be constructed in various ways,depending upon the particular processing functions that are intended tobe performed.

In the illustrated embodiment (see FIGS. 10 and 11), the modules 424 and426 take the form of fluid circuit bags 434 and 436. Each bag 434 and436 is formed, e.g., by radio frequency welding together two sheets ofmedical plastic material (e.g., polyvinyl chloride). Each bag 434 and436 includes an interior array of radio frequency seals forming fluidpaths, chamber regions, sensor regions, and clamp regions.

In the illustrated embodiment, when secured to the interior surface 404of the frame 400 (see FIGS. 7 and 9), the bag 434 rests over the bag436, so that portions of the fluid circuits defined by the modules 424and 426 overlay one another. As will be explained later, this makespossible synchronization of different processing functions using commonhardware elements on the machine 16.

II. Telemetry for the System

The system 10 can also include a telemetry network 22 (see FIGS. 1 and18). The telemetry network 22 provides the means to link the machine 16in communication with other locations 254 via, e.g., cellular networks,digital networks, modem, Internet, or satellites. A given location 254can, for example, receive data from the machine 16 at the treatmentlocation or transmit data to a data transmission/receiving device 296 atthe treatment location, or both. A main server 256 can monitor operationof the machine 16 or therapeutic parameters of the person undergoing thespecified treatment. The main server 256 can also provide helpfulinformation to the person undergoing the specified treatment. Thetelemetry network 22 can download processing or service commands to thedata receiver/transmitter 296.

1. Remote Information Management

FIG. 18 shows a representative telemetry network 22 in association witha machine 16 that carries out a specified treatment modality. Thetelemetry network 22 includes the data receiver/transmitter 296 coupledto the machine 16. The data receiver/transmitter 296 can be electricallyisolated from the machine 16, if desired. The telemetry network 22 alsoincludes a main data base server 256 coupled to the datareceiver/transmitter 296 and an array of satellite servers 260 linked tothe main data base server 256.

The data generated by the machine 16 during operation is processed bythe data receiver/transmitter 296. The data is stored, organized, andformatted for transmission to the main data base server 256. The database server 256 further processes and dispenses the information to thesatellite data base servers 260, following pre-programmed rules, definedby job function or use of the information. Data processing to suit theparticular needs of the telemetry network 22 can be developed andmodified without changing the machine 16.

The main data base server 256 can be located, e.g., at the company thatcreates or manages the system 10. The satellite data base servers 260can be located, for example, at the residence of a designated remotecare giver for the person, or at a full time remote centralizedmonitoring facility staffed by medically trained personnel, or at aremote service provider for the machine 16, or at a company thatsupplies the machine 16 or the processing cartridge 18.

Linked to the telemetry network 22, the machine 16 acts as a satellite.The machine 16 performs specified therapy tasks while monitoring basicsafety functions and providing the person at the treatment locationnotice of safety alarm conditions for resolution. Otherwise, the machine16 transmits procedure data to the telemetry network 22. The telemetrynetwork 22 relieves the machine 16 from major data processing tasks andrelated complexity. It is the main data base server 256, remote from themachine 16, that controls the processing and distribution of the dataamong the telemetry network 22, including the flow of information anddata to the person undergoing therapy. The person at the treatmentlocation can access data from the machine 16 through the local datareceiver/transmitter 296, which can comprise a laptop computer, handheldPC device, web tablet, cell phone, or any unit capable of dataprocessing.

The machine 16 can transmit data to the receiver/transmitter 296 invarious ways, e.g., electrically, by phone lines, optical cableconnection, infrared light, or radio frequency, using cordlessphone/modem, cellular phone/modem, or cellular satellite phone/modem.The telemetry network 22 may comprise a local, stand-alone network, orbe part of the Internet.

For example, when the machine 16 notifies the person at the treatmentlocation of a safety alarm condition, the safety alarm and itsunderlying data can also be sent to the main server 256 on the telemetrynetwork 22 via the receiver/transmitter 296. When an alarm condition isreceived by the main server 256, the main server 256 can locate anddownload to the receiving device 296 the portion of the operator'smanual for the machine that pertains to the alarm condition. Based uponthis information, and exercising judgment, the operator/user canintervene with operation of the machine 16. In this way, the main server256 can provide an automatic, context-sensitive help function to thetreatment location. The telemetry network 22 obviates the need toprovide on-board context-sensitive help programs for each machine 16.The telemetry network 22 centralizes this help function at a singlelocation, i.e., a main server 256 coupled to all machines 16.

The telemetry network 22 can relay to an inventory server 262 supply andusage information of components used for the treatment modality. Theserver 262 can maintain treatment site-specific inventories of suchitems, such as cartridges 18, ancillary processing materials, etc. Thecompany or companies that supply the machine 16, the processingcartridge 18, or the ancillary processing material to the treatmentlocation 12 can all be readily linked through the telemetry network 22to the inventory server 262. The inventory server 262 therebycentralizes inventory control and planning for the entire system 10,based upon information received in real time from each machine 16.

The telemetry network 22 can relay to a service server 264 hardwarestatus information for each machine 16. The service server 264 canprocess the information according to preprogrammed rules, to generatediagnostic reports, service requests or maintenance schedules. Thecompany or companies of the system 10 that supply or service the machine16 can all be readily linked through the telemetry network 22 to theservice server 264. The service server 264 thereby centralizes service,diagnostic, and maintenance functions for the entire system 10.Service-related information can also be sent to the treatment location12 via the receiving device 296.

The telemetry network 22 can also relay to a treatment monitoring server266, treatment-specific information pertaining to the therapy providedby each machine 16. Remote monitoring facilities 268, staffed bymedically trained personnel, can be readily linked through the telemetrynetwork 22 to the treatment monitoring server 266, which centralizestreatment monitoring functions for all treatment locations served by thesystem 10.

The telemetry network 22 can also provide through the device 296 anaccess portal for the person undergoing treatment to the myriad servicesand information contained on the Internet, e.g., over the web radio andTV, video, telephone, games, financial management, tax services, groceryordering, prescriptions purchases, etc. The main server 256 can compilediagnostic, therapeutic, and/or medical information to create a profilefor each person served by the system 10 to develop customized contentfor that person. The main server 256 thus provide customized ancillaryservices such as on line training, billing, coaching, mentoring, uplinksto doctors, links to patient communities, and otherwise provide avirtual community whereby persons using the system 10 can contact andcommunicate via the telemetry network 22.

The telemetry network 22 thus provides the unique ability to remotelymonitor equipment status, via the internet, then provide information tothe user, also via the internet, at the location of the equipment. Thisinformation can include, e.g., what page of the operator's manual wouldbe the most helpful for their current operational situation, actual dataabout the equipment's performance (e.g., could it use service, or is itset up based on the caretaker's recommendations), data about the currentsession, i.e., buttons pressed, alarms, internal machine parameters,commands, measurements.

The remote site can monitor the equipment for the same reasons that theuser might. It can also retrieve information about the machine 16 whenit is turned off because the telemetry device is self-powered. Itretains all information about the machine over a period of time (muchlike a flight recorder for an airplane).

2. On-Site Programming

The main server 256 on the telemetry network 22 can also store anddownload to each machine 16 (via the device 296) the system controllogic and programs necessary to perform a desired treatment modality.Programming to alter a treatment protocol to suit the particular needsof a single person at a treatments site can be developed and modifiedwithout a service call to change the machine 16 at any treatmentlocation, as is the current practice. System wide modifications andrevisions to control logic and programs that condition a machine 16 toperform a given treatment protocol can be developed and implementedwithout the need to retrofit each machine 16 at all treatment locationsby a service call. This approach separates the imparting of controlfunctions that are tailored to particular procedures, which can bedownloaded to the machine 16 at time of use, from imparting safetyfunctions that are generic to all procedures, which can be integrated inthe machine 16.

Alternatively, the control logic and programs necessary to perform adesired treatment protocol procedure can be carried in a machinereadable format on the cartridge 18. Scanners on the machine 16automatically transfer the control logic and programs to the machine 16in the act of loading the cartridge 18 on the machine 16. Bar code canbe used for this purpose. Touch contact or radio frequency siliconmemory devices can also be used. The machine 16 can also include localmemory, e.g., flash memory, to download and retain the code.

For example, as FIG. 2 shows, the machine 16 can include one or morecode readers 270 on the chassis panel 26. The frame 400 carries, e.g.,on a label or labels, a machine readable (e.g., digital) code 272 (seeFIG. 3) that contains the control logic and programs necessary toperform a desired treatment protocol using the cartridge 18. Loading thecartridge 18 on the machine 16 orients the code 272 to be scanned by thereader(s) 270. Scanning the code 272 downloads the control logic andprograms to memory. The machine 16 is thereby programmed on site.

The code 272 can also include the control logic and programs necessaryto monitor use of the cartridge 18. For example, the code 272 canprovide unique identification for each cartridge 18. The machine 16registers the unique identification at the time it scans the code 272.The machine 16 transmits this cartridge 18 identification information tothe main server 256 of the telemetry network 22. The telemetry network22 is able to uniquely track cartridge 18 use by the identification codethroughout the system 10.

Furthermore, the main server 256 can include preprogrammed rules thatprohibit multiple use of a cartridge 18, or that limit extended uses toa prescribed period of time. An attempted extended use of the samecartridge 18 on any machine 16, or an attempted use beyond theprescribed time period, will be detected by the machine 16 or the mainserver 256. In this arrangement, the machine 16 is disabled until anunused cartridge 18 is loaded on the machine 16.

Prior to undertaking set up pressure testing and priming of thecartridge 18, the machine 16 can also be conditioned to sense, e.g., byultrasonic means, the presence of fluid in the cartridge. The presenceof fluid indicates a reprocessed cartridge. In this arrangement, themachine 16 is disabled until a dry, unused cartridge 18 is loaded on themachine 16.

Service cartridges can also be provided for the machine 16. A servicecartridge carries a code that, when scanned by the reader or readers onthe chassis panel 26 and downloaded to memory, programs the machine 16to conduct a prescribed service and diagnostic protocol using theservice cartridge 18.

III. Representative Systems for Conducting Hemofiltration

The particular configuration of the machine 16 and the fluid processingcircuit 420, which the tubing 418 and flexible fluid circuit 408 form,can vary according to the processing objectives of the system 10. Asbefore stated, the system 10 is well suited for treatment modalitiesduring which one fluid is removed from the body and replaced withanother fluid in a controlled fashion, e.g., hemofiltration (HF),hemodialysis (HD), hemodialysis with hemofiltration (HDF), andperitoneal dialysis (PD).

For the purpose of illustration, FIG. 12 schematically shows a fluidcircuit FC(HF) for carrying out hemofiltration. The fluid circuit FC(HF)supports the removal of blood from an individual and the separation ofwaste fluid from the blood using a hemofilter 34. The fluid circuitFC(HF) also supports the return of treated blood and replacement fluidto the individual. The fluid circuit FC(HF) also supports anultrafiltration function.

The flexible fluid circuit 420 carried by the frame 400 and the machine16 can be readily configured to form this circuit FC(HF) and therebyconduct hemofiltration. A person of skill in the art will readilyappreciate how the fluid circuit 420 and machine 16 can be configured toperform other treatment modalities, as well.

In the illustrated implementation, the first module 424 is configured tohandle waste fluid, and the second module 426 is configured to handlereplacement fluid.

As FIG. 10 shows, the waste fluid management module 424 includes fluidwaste balancing chambers 212R/214R and associated waste fluid clampregions 220 and 222. The location of these elements in the fluid circuitFC(HF)are also shown schematically in FIG. 12.

As FIG. 11 shows, the replacement fluid management module 426 includescorresponding replacement fluid balancing chambers 212F/214F andassociated replacement fluid clamp regions 224 and 226. The location ofthese elements in the fluid circuit FC(HF)are also shown schematicallyin FIG. 12.

When the modules 424 and 426 are mounted against the interior surface404 of the frame 400 (see FIG. 9), the chambers 212R/214R and 212F/214Fand the clamp regions 222/220 and 224/226 communicate in the same plane.When the frame 400 is mounted for use on the machine 16, the overlayingchambers 212R/214R and 212F/214F and clamp regions 222/220 and 224/226operatively engage common machine elements on the machine 16 to carryout volumetric fluid balancing of replacement fluid in proportion towaste removal, without use of weight sensors. When the frame 400 ismounted for use on the machine 16, the modules 424 and 426, inassociation with hardware elements on the machine 16, also accomplishultrafiltration.

In the illustrated embodiment (see FIGS. 7 and 8), an exterior surface406 of the frame 400 is slightly recessed or concave. When the frame 400is mounted on the machine 16, this recessed frame surface 406 nestswithin a correspondingly raised surface 407 on the door 28 (see FIG.13). When so nested, convex or domed frame regions 412, which projectabove the surface 406 of the frame 400 (see FIGS. 7 and 8) fit withinmating concave indentations 206′ and 208′ on the door 28.

The fluid balancing chambers 212R/214R and 212F/214F rest in anoverlying relationship within these domed regions 412 on the oppositeinterior surface 404 of the frame 400 (see FIG. 8). When the frame 400is mounted on the machine 16, and the door 28 closed, the interiorsurface 404 faces the chassis panel 28, and the fluid balancing chambers212R/214R and 212F/214F rest within concave indentations 206 and 208formed on the chassis panel 26 (see FIG. 2). When the frame 400 ismounted on the machine 16, and the door 28 closed, the flexible chambers212R/214R and 212F/214F are thereby enclosed between the indentations206/208 on the chassis panel 26 and the convex regions 412 of the frame400 (which themselves nest within the concave indentations 206′/208′ onthe door 28). Expansion of the flexible chambers 212R/214R and 212F/214Fas a result of fluid introduction is thereby restrained to a knownmaximum volume, generally approximately between 10 and 50 cc, preferablyapproximately between 20 and 40 cc, more preferably approximately 25 cc,defined between the chassis chambers 206/208 and the convex frameregions 412.

As FIG. 8 shows, cut-outs 410 in the surface 406 expose the overlayingflexible clamp regions 222/220 and 224/226 to contact with the fourclamping pads 450 mounted on the door 28 (see FIG. 13) and hardwareclamping elements 244, 246, 248, and 250 on the chassis panel 26 (seeFIG. 2). In operation, the clamping elements 244, 246, 248, and 250 arecaused to project from the chassis panel 26 to press the overlying clampregions 222/220 and 224/226 against the clamping pads 450 on the door28. Synchronized valve functions are thereby made possible, as will bedescribed later.

Referring back to FIG. 8, another cut-out 413 in the surface 406 exposesa portion of the fluid circuit 408 for blood leak sensing functions, aswill also be described later.

Surrounding the surface 406 are recessed channel regions 414 a to 414 j,which are formed in the exterior surface 402. These recessed channelregions 414 a to 414 j (identified in FIG. 8) accommodate the passage ofthe lengths of flexible tubing 418 that communicate with the flexiblefluid circuit 408, to form the fluid processing circuit 420. Therecessed regions 414 a to 414 j form channels that guide and restrainthe tubing 418 within the frame 400. Multiple cut-outs 442 a to 442 iare formed along the recessed regions 414 a to 414 j, to exposeintervals of the tubing 418 for engagement with clamps or sensors on themachine 16, as will be described.

As FIGS. 7 show, a cover member 416 made, e.g., from rigid or semi-rigidpaper or plastic, is desirably secured to the exterior surface 402 ofthe frame 400 to overlay and close the recessed channel regions 414, inwhich the tubing 418 is carried (FIG. 3 shows the exterior surface 402with the cover member 416 installed).

As FIG. 8 shows, portions of tubing 418 extend beyond the support frame400 for connection with the patient and other external items making upthe fluid processing circuit 420, as will be described later. Cartridge18 may extend beyond the edge of machine 16.

Portions of the tubing 418 also communicate with peristaltic pump tubes94, 145, 155, and 201 located in the surface 406 (see FIG. 8). Cut-outs446 a to 446 c are formed in the region 406 beneath the pump tubes 94,145, 155, and 201, to expose the pump tubes 94, 145, 155, and 201 forengagement with the corresponding peristaltic pump rollers 92, 144, and152 on the chassis panel 26 (see FIG. 2) and the corresponding pumpraces 362 on the door 28 (see FIG. 13).

Further regarding the configuration of the fluid processing circuit 420(see FIG. 8), as adapted to conform to the hemofiltration circuit FC(HF)shown in FIG. 12, the flexible tubing 72 forms the arterial blood supplypath, with an appropriate distal connector to couple to an arterialblood access site. The tubing 72 is guided by a recessed channel 414 ainto the frame 400. Cut-outs 442 a and 442 b expose the tubing 72 forengagement with an arterial blood line air sensor 98 and arterial bloodline clamp 96.

The tubing 72 is coupled with the pump tube 94, which spans the cut-out446 a in the frame 400, for engagement with the blood pump 92 on thechassis panel 26 (see FIG. 2).

Tubing 78 extends from the pump tube region 94 in a recessed channel 414b in the frame 400. The tubing 78 extends beyond the frame 400 andincludes the connector 82 to couple the arterial blood path to the inletof a hemofilter 34 (see FIG. 12).

The placement of the cut-out 442 a (and associated air sensor 98 on themachine 16) upstream of the hemofilter 34 allows air bubbles to bedetected prior to entering the hemofilter 34. This location isdesirable, because, in the hemofilter 34, air bubbles break up into tinymicro-bubbles, which are not as easily detected as bubbles upstream ofthe hemofilter 34. Placement of the air sensor 98 upstream of thehemofilter 34 also serves the additional purpose of detecting air whenthe blood pump 92 is operated in reverse, to rinse back blood to thepatient. The air sensor 98 also detects if the arterial blood line isclamped or otherwise occluded, to thereby allow terminate operation ofthe arterial blood pump 92 when this condition occurs. Air sensor 98 canalso sense a clamped or occluded arterial line while the pump turns. Theresulting negative pressure degasses the blood which is sensed by theair sensor, and an alarm is sounded. If air by chance enters thearterial blood line, e.g., by a faulty connection or an air leak, theair sensor 98 will detect this condition and terminate operation of thearterial blood pump before the air enters the hemofilter.

As FIG. 8 shows, the tubing 84 extends beyond the frame 400 and includesa distal connector 86 to couple to the blood outlet of the hemofilter 34(see FIG. 12). The tubing 84 is led across the frame 400 through arecessed channel 414 c. Cut-away regions 442 c and 442 d on the frame400 expose the tubing 84 for engagement with the venous blood line airsensor 108 and venous S blood line clamp 112 (see FIG. 12). The tubing84 then extends beyond the frame 400, and carries an appropriate distalconnector to couple to venous blood access site.

As FIG. 8 shows, the flexible tubing 118 extends beyond the frame 400and carries a distal connector 120 to couple to the waste outlet of thehemofilter 34 (see FIG. 12). The tubing 118 thereby serves to conveywaste fluid for fluid balancing and discharge. The flexible tubing 118enters a recessed channel 414 d in the frame 400 and joins a connectorC8. The connector C8 couples the tubing 118 to the waste fluidmanagement module 424, and through the module 424 to ultrafiltrationpump tube 145 (through connector C1) and the waste pump tube 155(through connector C7). The pump tube 145 spans a cut-out 446 b in theframe 400 to connector C2, for engagement with the ultrafiltration pump144 on the chassis panel 26 (see FIG. 2). The pump tube 155 spans a cutaway region 446c in the frame 400 to connector C3, for engagement withthe waste fluid header region 154 of the dual header waste andreplacement pump 152 on the chassis panel 26 (see FIG. 2).

Connectors C2 and C3 are fluidically coupled via the waste fluidmanagement module 424 (see FIG. 10) to connectors C10 and C4. As FIG. 8shows, the flexible tubing 122 is coupled by the connector C4 to anoutlet of the waste management module 424. The tubing 122 is guidedthrough a recessed channel 414 e in the support frame 400. Cut-awayregion 442 e on the frame 400 expose the tubing 122 for engagement withthe waste line clamp 166. The tubing 122 then extends beyond the frame400, with an appropriate distal connector 124 to couple to a waste bagor an external drain. It is through this tubing 122 that waste fluid isdischarged after fluid balancing. An in-line air break 170 (see FIG. 12)can be provided in communication with the tubing 122 downstream of thewaste clamp 166, to prevent back flow of contaminants from the waste bagor drain.

Referring to FIG. 8, the flexible tubing 172 serves to conveyreplacement fluid. The tubing 172 extends outside the frame 400 andincludes a distal connector 174 that enables connection to multiplecontainers of replacement fluid 176 (see FIG. 12). The tubing 172 isguided by a recessed channel 414 f within the frame 400. Cut-awayregions 442 f and 442 g on the frame 400 expose the tubing 172 forengagement with an in line air sensor 182 and replacement fluid clamp188 (see FIG. 12).

Flexible tubing 430 is guided through a recessed channel 414 g in thesupport frame 400 between two t-connectors, one in the arterial bloodtubing 72 and the other in the replacement tubing 172. The tubing 430serves as the priming or bolus branch path 192, as will be described. Acut-away region 442 h on the frame 400 exposes the tubing 430 forengagement with the priming clamp 194 on the machine 16 (see FIG. 12).

The replacement fluid tubing 172 is further guided by the recessedchannel 414 h in the frame 400 to the replacement fluid pump tube 201(previously described), which is also coupled via a connector C5 to thereplacement fluid management module 426 of the flexible fluid circuit408. As FIG. 11 also shows, connector C5 is also fluidically coupled viathe replacement fluid management module 426 to the connectors C6 and C9.The pump tube 201 spans the cut away region 446 d in the frame 400, forengagement with the replacement fluid header region 200 of the dualheader waste and replacement pump 152 on the chassis panel 26 (see FIG.2).

Flexible tubing 432 is coupled by a connector C6 to the replacementfluid module 426. The flexible tubing 432 is guided through a recessedchannel 414 i in the support frame to a t-connector, which joins thereplacement tubing 172 in the region immediately downstream of theconnection with the replacement fluid pump tube 201. The tubing 432serves as the relief path 240 that prevents overfilling of the fluidbalancing compartments, as will be described.

Flexible tubing 428 is coupled by a connector C9 to the replacementfluid management module 426. The tubing 428 is guided through a recessedchannel 414 j in the support frame 400 in a small loop outside the frame400 and is coupled by a t-connector to the venous blood return tubing84. It is through this path that replacement fluid is added to thevenous blood being returned to the patient.

The bags 434 and 436 are secured in overlaying alignment to the interiorsurface 404 of the frame 400 by the connectors C1 to C10, previouslydescribed.

FIG. 10 shows the waste management fluid circuit contained in the bag434, as it would appear if viewed from interior surface 404 of thesupport frame 400 (as FIG. 9 also shows). The bag 434 is shown inassociation with the ultrafiltration pump tube 145 and waste fluid pumptube 155 that are also carried on the region 406 of the support frame400.

The fluid circuit in the bag 434 includes the waste path 138 that leadsto the waste side compartments 212R and 214R (for fluid balancing) byway of the waste pump 155 and the waste path 136 by way of theultrafiltration pump 145 that bypasses the waste side compartments 212Rand 214R (for ultrafiltration). The flow paths in the waste fluidcircuit in the bag 434 also include the exposed waste inlet clampregions 220, to engage the valve assemblies 246 and 248 to controlinflow of waste fluid into the waste compartments 212R and 214R, and theexposed waste outlet clamp regions 222, to engage the valve assemblies244 and 250 to control outflow of waste fluid from the wastecompartments 212R and 214R. The fluid circuit also includes the pressuresensor region 160, to engage the pressure sensor 156 (see FIG. 15)downstream of the waste and replacement fluid pump 152.

FIG. 11 shows the replacement fluid management circuit contained in thebag 436, as it would appear if viewed from the interior surface 404 ofthe support frame 400 (as FIG. 8 also shows). The bag 436 is shown inassociation with the replacement fluid pump tube 201 that is alsocarried in the region 406 of the support frame 400. The replacementfluid pump tube 201 is located alongside the waste fluid pump tube 155,on region 200 for concurrent engagement with the dual header waste andreplacement pump 152 on the chassis panel 26 (see FIG. 2).

The fluid circuit in the bag 436 includes the replacement fluid pathswhich lead to and from the replacement side compartments 212F and 214F.The fluid circuit also includes the inlet clamp regions 224, to engagethe valve assemblies 244 and 250 on the machine 16 to control inflow ofreplacement fluid into the replacement side compartments 212F and 214F;and the outlet clamp regions 226, to engage the valve assemblies 246 and248 on the machine 16 to control outflow of replacement fluid from thereplacement side compartments 212F and 214F. The fluid circuit includesa sensor region 204, to engage the pressure sensor 202 (see FIG. 15)downstream of the waste and replacement pump 152.

When the bags 434 and 436 are mounted in overlaying relationship on theinterior frame surface 404 (as FIG. 9 shows), the replacement sidecompartments 212F and 214F and the waste side compartments 212R and 214Rtogether rest in the convex recesses 412 in the region 406 of theexterior frame surface 402. The inlet clamp regions of the wastecompartments 212R and 214R formed on the waste panel 234 overlay theoutlet clamp regions of the replacement compartments 212F and 214Fformed on the replacement panel 232, and vice versa.

The entry and exit paths serving the waste and replacement compartmentsformed in the bags 434 and 436 (shown in FIG. 9) are all located at thetop of the chambers 212R, 214R, 212F, and 214F. Priming is achieved, asthe paths are top-oriented. Furthermore, due to the overlayingrelationship of bags 434 and 436, the clamping regions 220, 222, 224,and 226 are arranged to overlay one another. The overlaying arrangementof the clamping regions 220, 222, 224, and 226 serving the waste andreplacement compartments simplifies the number and operation of theinlet and outlet valve assemblies 216 and 218 on the machine 16. Sincethe inlet clamp regions 224 for the replacement compartments 212F and214F overlay the outlet clamp regions 222 for the waste compartments212R and 214R, and vice versa, only four clamping elements 244, 246,248, 250 need be employed to simultaneously open and close theoverlaying eight clamp regions.

1. Achieving Synchronized Volumetric Fluid Balancing

In use, as FIG. 14 shows, the first clamping element 244 is movable intosimultaneous clamping engagement with the inlet clamp region 224 of thereplacement compartment 212F (in the replacement fluid module bag 436)and the outlet clamp region 222 of the waste compartment 212R (in thewaste fluid module bag 434), closing both. Likewise, the fourth clampingelement 250 is movable into simultaneous clamping engagement with theinlet clamp region 224 of the replacement compartment 214F (in thereplacement fluid module bag 436) and the outlet clamp region 222 of thewaste compartment 214R (in the waste fluid module bag 434).

The second clamping element 246 is movable into simultaneous clampingengagement with the outlet clamp region 226 of the replacementcompartment 212F and the inlet clamp region 220 of the waste compartment212R, closing both. Likewise, the third clamping element 248 is movableinto simultaneous clamping engagement with the outlet clamp region 226of the replacement compartment 214F and the inlet clamp region 220 ofthe waste compartment 214R, closing both.

The machine 16 toggles operation of the first and third clampingelements 244, 248 in tandem, while toggling operation the second andfourth clamping elements 246, 250 in tandem. When the first and thirdclamping elements 244, 248 are operated to close their respective clampregions, replacement fluid enters the replacement compartment 214F todisplace waste fluid from the underlying waste compartment 214R, whilewaste fluid enters the waste compartment 212R to displace replacementfluid from the overlaying replacement compartment 212F. When the secondand fourth clamping elements 246, 250 are operated to close theirrespective clamp regions, replacement fluid enters the replacementcompartment 212F to displace waste fluid from the underlying wastecompartment 212R, while waste fluid enters the waste compartment 214R todisplace replacement fluid from the overlaying replacement compartment214F.

FIGS. 15 and 16 show a mechanically linked pump and valve system 300that can be arranged on the chassis panel 26 of the machine 16 and usedin association with the flexible fluid circuit 408.

The system 300 includes three electric motors 302, 304, and 306. Thefirst motor 302 is mechanically linked by a drive belt 308 to a dualheader waste and replacement pump 152. The second motor 304 ismechanically linked by a drive belt 310 to a blood pump 92. The thirdmotor 306 is mechanically linked by a drive belt 312 to aultrafiltration pump 144.

A drive belt 314 also mechanically links the first motor to the first,second, third, and fourth clamping elements 244, 246, 248, and 250, viaa cam actuator mechanism 316. The cam actuator mechanism 316 includes,for each clamping element 244, 246, 248, and 250 a pinch valve 318mechanically coupled to a cam 320. The cams 320 rotate about a driveshaft 322, which is coupled to the drive belt 314.

Rotation of the cams 320 advances or withdraws the pinch valves 318,according to the surface contour machined on the periphery of the cam320. When advanced, the pinch valve 318 closes the overlying clampregions of the fluid circuit module bags 424 and 426 that lay in itspath. When withdrawn, the pinch valve 318 opens the overlying clampregions.

The cams 320 are arranged along the drive shaft 322 to achieve apredetermined sequence of pinch valve operation. During the sequence,the rotating cams 320 first simultaneously close all the clampingelements 244, 246, 248, and 250 for a predetermined short time period,and then open clamping elements 244 and 248, while closing clampingelements 246 and 250 for a predetermined time period. The rotating cams320 then return all the clamping elements 244, 246, 248, and 250 to asimultaneously closed condition for a short predetermined time period,and then open clamping elements 246 and 250, while closing clampingelements 244 and 248 for a predetermined time period.

The sequence is repeated and achieves the balanced cycling ofreplacement fluid and waste fluid through the module bags 424 and 426,as previously described. A chamber cycle occurs in the time intervalthat the valve elements 244, 246, 248, and 250 change from asimultaneously closed condition and return to the simultaneously closedcondition.

In a preferred embodiment (see FIG. 17), each clamping element 244, 246,248, and 250 comprises a valve pin 500 movable within a valve slot 506in the chassis panel 26. A rotating bearing surface 502 at one end ofthe valve pin 500 rides on the cam surface 504 of the correspondingrotating cam 320. As the cam 320 rotates, the cam surface 504 presentsregions of increasing or decreasing radius, causing the pin 500 toreciprocate within the valve slot 506 toward and away from the door 28,which, during use of the fluid circuit 408, faces the chassis panel 26in the closed position.

A pinch valve 318 is carried at the opposite end of the valve pin 500.The pinch valve 318 includes a pinch valve chamber 508, in which thevalve pin 500 rests. A spring 510 in the pinch valve chamber 508 couplesthe pinch valve 318 to the valve pin 500. The spring 510 applies a fixedvalve force against the pinch valve 318, in the absence of physicalcontact between the end of the valve pin 500 and the pinch valve 318.The spring 510 thereby mediates against over- and under-valving effectsas a result of small changes in tolerance between the pin 500 and pinchvalve 318, fluid circuit module bag 424 and 426 thickness, and theclosed gap between door 28 and chassis 26.

When mounted for use on the chassis panel 26, with the door 28 closed,the fluid circuit 408 is sandwiched between the panel 26 and the door28. Each pinch valve 318 is aligned with a valve plate 512 carried bythe door 28. The valve plate 512 is made from a hard plastic or metallicmaterial. The valve plate 512 rests against a disk 514 on the door 28,which can be made of rubber or another elastomeric material. The disk514, which can also be a spring, allows the valve plate 512 to move or“float” when the pinch valve applies a valve force. The valve plate 512thereby accounts for any lack of perpendicularity between the pinchvalve 318 and the valve plate 512.

Movement of the pinch valve 318 toward the door 28 (as the cam surface504 presents regions of increasing radius) pinches the intermediate,aligned clamp region in the fluid circuit 56 (comprised of modules 424and 426 overlying one another) between the pinch valve 318 and the valveplate 512, thereby closing the valve region. Likewise, movement of thepinch valve 318 toward the door 28 (as the cam surface 504 presentsregions of decreasing radius) separates the pinch valve 318 from thevalve plate 514, thereby opening the intermediate valve region. The camactuator mechanism 316 mechanically links the clamping elements 244,246, 248, and 250 ratiometrically with the first motor 302. As the motor302 increases or decreases the speed of the dual header waste andreplacement pump 152, the operation of the clamping elements 244, 246,248 and 250 increases or decreases a proportional amount.

In a preferred embodiment, the ratio is set so that the flow rate perunit time through the waste pump header region 154 (i.e., through wastepath 434) approximately equals three-fourths of the volume of the wastecompartment 212R/214R, while maintaining the cycle rate of 10 cycles perminute for a waste fluid flow rate of approximately 200 ml/min. Forexample, if the chamber volume is 25 cc, the cycle occurs after 18 to 21cc of waste fluid enters the compartment. In other embodiments, thecycle rate is 9–11 cycles per minute for a waste fluid flow rate ofapproximately 180–220 ml/min, or the cycle rate is 8–12 cycles perminute for a waste fluid flow rate of approximately 160–240 ml/min.

In the illustrated embodiment, the waste pump header 155 is made smallerin diameter than the replacement fluid header 201. Thus, duringoperation of the dual header pump 152, which is made up of pump regions154 and 200, the flow rate through the replacement fluid header region200/201 (through replacement fluid path 426) will always be larger thanthe flow rate through the waste pump header region 154/155 (throughwaste path 424). Due to the higher flow rate through the replacementfluid path 426, a pressure relief path 438 (see FIG. 11) and 432 (seeFIGS. 12 and 8) with pressure relief bypass valve 242 (see FIG. 15) isprovided, to prevent overfilling. In the illustrated embodiment, thevalve 242 is a mechanically spring biased pressure regulator, and servesthe pressure regulation and bypass function of the machine 16.

In this arrangement, the in-line compartment that receives waste fluidwill fill to approximately three-fourths of its volume during eachcycle, displacing an equal amount of replacement fluid from itscompanion compartment. At the same time, the other in-line compartmentthat receives replacement fluid will fill completely. If the compartmentcompletely fills with replacement fluid before the end of the cycle, thepressure relief bypass valve 242 (see FIG. 15) will open to circulatereplacement fluid through the relief path 240, made up of 438, C6, and432 (see FIG. 12), to prevent overfilling. During the next cycle, wastefluid in the compartment will be completely displaced by the completefill of replacement fluid in its companion compartment.

The provision of a higher flow rate in the replacement fluid path alsofacilitates initial priming (as will be described later). only severalchamber cycles are required to completely prime the in-line containers212 and 214 with replacement fluid before fluid balancing operationsbegin.

The pump and valve system 300 used in association with the fluid circuit408 achieves accurate fluid balancing, e.g., during hemofiltration,hemodialysis, hemodialysis with hemofiltration, and peritoneal dialysis.

B. Fluid Flow Path Dimensions

In one embodiment, key functional regions within the flexible fluidcircuits are formed to possess dimensions that lay within criticalranges, to thereby achieve desired fluid flow conditions, pressuresensing conditions, fluid balancing functions, and valve functions. Forexample, each fluid balancing chamber 212 F/R and 214 F/R is formed tohave a height (measured between the bottom of the chamber and the clampregions) of between about 3.25 inches and about 5.0 inches, with anominal height of about 3.6 inches. In this embodiment, each fluidbalancing chamber 212 F/R and 214 F/R is formed to have a width(measured between the sides of the chamber and determined by the widthof pinch clamp 318) of between about 1.0 inch and about 2.75 inches,with a nominal width of about 1.2 inches. These dimensions help optimizevolumetric fluid balance functions.

Further, in another embodiment, each clamp region 220/222 and 224/226 isformed to have a channel width of between about 0.10 inch and 0.40 inch.Bead suppression measures are employed in the clamp regions 220/222 and224/226 to keep the material adjacent the welded seams, which form theclamp regions, from exceeding more than twice the thickness of thematerial walls. These steps assure reliable functioning of theoverlaying clamp regions in association with the external clamps.

Also, in another embodiment, the ultrafiltration fluid path 136 isformed to have a channel width of greater than about 0.140 inch but lessthan about 0.60 inch. This optimizes the flow of waste fluid.

In a preferred embodiment, the regions where pressure is sensed in thefluid circuit is formed to have in an interior diameter that is greaterthan 0.40 inch, to optimize pressure sensing without an air-bloodinterface using external sensors.

Also in a preferred embodiment, the passage 438 in the replacement fluidmanagement module 426 that leads to the bypass tubing 432 (see FIG. 11)is formed with a channel width of between about 0.050 inch and 0.60inch. The width is matched with pinch portion of regulator 242. Thisestablishes the proper balanced flow conditions to prevent chamberoverfilling. The foregoing dimensions and ranges are set forth solelyfor the purpose of illustrating typical device dimensions. The actualdimensions of a device constructed according to the principles of thepresent invention may obviously vary outside of the listed rangeswithout departing from those basic principles.

C. Representative Hemofiltration Modalities

During hemofiltration, blood is drawn from the person at a prescribedflow rate (BFR). Waste fluid is removed from the blood flow throughfilter 34 and volumetrically balanced with replacement fluid, which isreturned in the venous blood flow at a prescribed rate (RFR). Aprescribed net ultrafiltration volume of waste fluid is also removed ata prescribed flow rate (UFR) with fluid balancing, to control net weightloss. Operation of the machine 16 in a hemofiltration mode terminateswhen either (i) the replacement fluid sensor indicates the absence ofreplacement fluid flow by sensing the presence of air (i.e., no morereplacement fluid) and the net ultrafiltration goal has been achieved;or (ii) the time prescribed for the session has elapsed.

Hemofiltration can also be performed without an ultrafiltration function(which can be called balanced hemofiltration). This mode can be used forpersons that experience no weight gains between treatment sessions. Thismode can also be used at the end of a hemofiltration session, when thenet ultrafiltration goal was achieved before exhausting the supply ofreplacement fluid.

During another hemofiltration modality (called only netultrafiltration), only a net ultrafiltration volume of waste is removedfrom the person. No fluid is replaced. This mode can be used when it isdesired only to remove fluid. This mode can also be used at the end of ahemofiltration session, when the net ultrafiltration goal has not beenachieved but the supply of replacement fluid has been exhausted.

In another hemofiltration modality (called replacement fluid bolus),there are no fluid balancing and ultrafiltration functions. Blood iscirculated in an extracorporeal path and a bolus of replacement fluid isadded. In the illustrated embodiment, the ultrafiltration pump 144 isrun in reverse at a speed equal to the waste and replacement pump 152.This recirculates waste fluid through the waste compartments 212R and214R, to add replacement fluid from the replacement compartments 212Fand 214F to the patient. The waste fluid that is recirculated limitswaste fluid removal through the hemofilter 34, yielding replacementfluid addition without additional waste fluid removal. The net volume ofadded replacement fluid conveyed to the patient equals the volume ofwaste fluid recirculated. This mode can be used to return fluid to aperson in a bolus volume, e.g., during a hypotensive episode or duringrinse back at the end of a given hemofiltration session.

1. Controlling the Blood Flow Rate

High blood flow rates (e.g., in some embodiments at least 200 ml/min ormore, in other embodiments at least 300 ml/min or more, in otherembodiments at least 400 ml/min or more, in other embodiments at least500 ml/min or more, and in other embodiments at least 600 ml/min ormore) are conducive to rapid, efficient frequent hemofiltration. Thehigh blood flow rates not only reduce the processing time, but alsosignificantly increases the transport rate of uremic toxins across thehemofiltration membrane. In this way, the system 10 removes highconcentrations of uremic toxins, without requiring the removal of highfluid volumes, with the attendant loss of electrolytes.

The blood flow rate (BFR) can be prescribed by an attending physicianand input by the operator at the beginning of a treatment session.Alternatively, the machine 16 can automatically control to achieve anoptimal BFR and minimize procedure time, based upon a desired filtrationfraction value (FF), ultrafiltration flow rate (UFR), and replacementfluid flow rate (RFR), as follows: BFR=(RFR+UFR)/FF.

where:

FF is the desired percentage of fluid to be removed from the bloodstream through the hemofilter 34.

A desired FF (typically 20% to 35%) for post dilution HF can be eitherpreset or prescribed by the attending physician. A desired FF takes intoaccount the desired therapeutic objectives of toxin removal, as well asthe performance characteristics of the hemofilter 34. A nominal FF canbe determined based upon empirical and observed information drawn from apopulation of individuals undergoing hemofiltration. A maximum value ofapproximately 30% is believed to be appropriate for most individuals andhemofilters 34, to achieve a desired therapeutic result without cloggingof the hemofilter 34.

In the illustrated embodiment, an arterial line sensor is incorporatedinto the extracorporeal circuit. The sensor 98 is an ultrasonic air leakdetector, which also can provide the added capacity to sense flow rate.

In the illustrated embodiment, the machine 16 senses waste fluidpressure to control the blood flow rate to optimize the removal of fluidacross the hemofilter 34. As arterial blood flows through the hemofilter34 (controlled by the blood pump 92), a certain volume of waste fluidwill cross the membrane into the waste line 118. The volume of wastefluid entering the waste line 118 depends upon the magnitude of thetransmembrane pressure, or the pressure differential between the bloodon the inside of filter fibers and the waste fluid on the outside of thefibers. As waste fluid is pumped away, the transmembrane pressureincreases pushing waste fluid across membrane to replace removed waste.The transmembrane pressure is sensed by the sensor 132. The waste fluidpressure is adjusted by controlling the waste fluid removal rate throughthe fluid balancing compartments (i.e., through control of the waste andreplacement pump 152) and through the UF pump 144.

The machine 16 monitors the waste fluid pressure at sensor 132. Bykeeping the pressure sensed by the sensor 132 slightly above zero(approximately 30 to 100 mmHg), the machine 16 achieves the maximumremoval of fluid from the blood at the operative blood flow rate. Wastepressure values significantly higher than zero will limit removal offluid from the blood and keep a higher percentage of waste fluid in theblood (i.e., result in a lower filtration fraction). However, this maybe desirable for persons who tend to clot easier. The machine 16 canalso include a waste pressure alarm to indicate when the sensed wastefluid pressure does not meet set criteria.

By sensing waste fluid pressure by sensor 132, the machine 16 alsoindirectly monitors arterial blood pressure and flow. At a constantblood pump speed, changes in arterial blood flow caused, e.g., by accessclotting or increased arterial blood pressure, makes less waste fluidavailable in the waste line 118. At a given speed for pump 152, changein arterial blood flow will lower the sensed waste pressure at sensor132 to a negative value, as fluid is now drawn across the membrane. Themachine 16 adjusts for the change in arterial blood flow by correctingthe waste fluid removal rate through the pump 152 and 144, to bring thewaste pressure back to slightly above zero, or to another set value.

In this arrangement, a pressure sensor in the arterial blood line is notrequired. If the arterial pressure increases at a fixed blood pumpspeed, the blood flow must drop, which will result in a sensed relateddrop in the waste fluid pressure by the sensor 132. Adjusting the pump152 and 144 to achieve a pressure slightly above zero corrects thereduced arterial blood flow. In this arrangement, since the waste fluidpressure is maintained at a slightly positive value, it is not possibleto develop a reverse transmembrane pressure, which conveys waste fluidback to the person's blood. The maximum transmembrane pressure is themaximum venous pressure, since waste fluid pressure is held slightlypositive.

In an alternative arrangement, arterial blood pressure can be measuredby a sensor located upstream of the blood pump. The rate of the bloodpump is set to maintain sensed arterial blood pressure at apredetermined control point. This controls the blood pump speed to amaximum rate. The control point can be determined, e.g., on a day-to-daybasis, to take into account the blood access function of the personundergoing treatment. Use of an arterial pressure control pointminimizes the treatment time, or, alternatively, if treatment time isfixed, the removal of waste fluid can maximized.

In this arrangement, safety alarms can be included should the sensedarterial pressure become more negative than the control point, alongwith a function to shut down the blood pump should an alarm occur.

In an alternative arrangement, a flow rate sensor can be placed in thearterial blood line to sense an actual blood flow rate. The sensed bloodflow rate is compared to a commanded blood flow rate, and the blood pumpis controlled to a commanded difference between the two flow rates. Inthis way, a maximum blood flow rate can be achieved. Alternatively, asarterial blood pressure can be expressed as a function of flow rate,arterial blood pressure can be derived from the sensed flow rate. Therate of the blood pump is set to maintain the derived arterial bloodpressure at a predetermined control point. This controls the blood pumpspeed to a maximum rate. As stated above, use of an arterial pressurecontrol point minimizes the treatment time, or, alternatively, iftreatment time is fixed, the removal of waste fluid can be maximized bycontrolling waste fluid pressure, as described above.

2. Controlling the Replacement Fluid Flow Rate

RFR can be prescribed by an attending physician and inputted by theoperator at the beginning of a treatment session.

Alternatively, the machine 16 can automatically control RFR to minimizeprocedure time based upon the desired filtration fraction value (FF),BFR, and UFR, as follows: RFR=(BFR*FF)−UFR.

In the illustrated embodiment, waste is conveyed to the waste sidecompartments 212R and 214R, and replacement fluid is conveyed to thereplacement side compartments 212F and 214F, by operation of the dualheader waste and replacement fluid pump 152. Alternatively, separatewaste and replacement fluid pumps can be provided.

The speed of the waste and replacement pump 152 is controlled to achievethe desired RFR. The machine 16 cycles the inlet and outlet valveassemblies 244, 246, 248, and 250, as described. The machine 16 cyclesbetween the valve states according to the speed of the waste and fluidpump 152 to avoid overfilling the compartments 212, 214 receiving fluid.Various synchronization techniques can be used.

In a preferred embodiment, the waste fluid is pumped at RFR, and thereplacement fluid is pumped at a higher rate, but is subject to pressurerelief through the pressure relief path 240 upon filling thecorresponding replacement side compartment 212F and 214F.

In another arrangement, the timing of the transition between valvecycles is determined by active sensing of pressure within thecompartments 212, 214 receiving liquid. As the two matching walls ofchambers 212R/212F and 214R/214F reach the end of their travels,pressure will increase, signaling an end of cycle to switch valvestates.

In yet another arrangement, the location of the two matching walls ofchambers 212R/212F and 214R/214F as they reach the end of their travelsare actively sensed by end of cycle sensors on the machine 16. Thesensors can comprise, e.g., optical sensors, capacitance sensors,magnetic Hall effect sensors, or by radio frequency (e.g., microwave)sensors. The termination of movement of the walls indicates the completefilling of a compartment and the concomitant emptying of the othercompartment, marking the end of a cycle. The sensors trigger an end ofcycle signal to switch valve states.

The machine 16 counts the valve cycles. Since a known volume ofreplacement fluid is expelled from a replacement side compartment duringeach valve cycle, the machine 16 can derive the total replacement volumefrom the number of valve cycles. The replacement fluid volume is alsoknown by the number of replacement fluid bags of known volume that areemptied during a given session.

Hemofiltration can be conducted without fluid replacement, i.e., onlynet ultrafiltration, by setting RFR to zero.

3. Controlling the Ultrafiltration Flow Rate

UFR can be prescribed by an attending physician and inputted by theoperator at the beginning of a treatment session.

The speed of the ultrafiltration pump is monitored and varied tomaintain UFR.

Frequent hemofiltration can be conducted without an ultrafiltrationfunction, i.e., balanced hemofiltration, by setting UFR to zero.

4. Active Filtration Rate Control

In an alternative embodiment, the machine 16 also actively controls thefiltration rate along with the blood flow rate, to achieve a desiredmagnitude of uremic toxin removal through the hemofilter 34.

In this embodiment, the machine 16 includes a flow restrictor which ispositioned to engage a region of the venous blood return path 84 in thecircuit 18. The restrictor comprises, e.g., a stepper-driven pressureclamp, which variably pinches a region of the venous blood return pathupon command to alter the outlet flow rate of blood. This, in turn,increases or decreases the transmembrane pressure across the filtermembrane.

For a given blood flow rate, waste transport across the filter membranewill increase with increasing transmembrane pressure, and vice versa.However, at some point, an increase in transmembrane pressure, aimed atmaximizing waste transport across the filter membrane, will drivecellular blood components against the filter membrane. Contact withcellular blood components can also clog the filter membrane pores, whichdecreases waste transport through the membrane.

Filtration rate control can also rely upon an upstream sensor mounted onthe machine 16. The sensor is positioned for association with a regionof the arterial blood supply path between the blood pump 92 and theinlet of the hemofilter 34. The sensor senses the hematocrit of theblood prior to its passage through the filter membrane (which will becalled the pre-treatment hematocrit). In the arrangement, a downstreamsensor is also mounted on the machine 16. The sensor is positioned forassociation with a region of the venous blood return path downstream ofthe outlet of the hemofilter 34. The sensor senses the hematocrit of theblood after its passage through the hemofilter 34 (which will be calledthe post-treatment hematocrit).

The difference between pre-treatment and post-treatment hematocrit is afunction of the degree of waste fluid removal by the hemofilter 34. Thatis, for a given blood flow rate, the more waste fluid that is removed bythe hemofilter 34, the greater the difference will be between thepre-treatment and post-treatment hematocrits, and vice versa. Themachine 16 can therefore derive an actual blood fluid reduction ratiobased upon the difference detected by sensors between the pre-treatmentand post-treatment hematocrits. The machine 16 periodically compares thederived fluid reduction value, based upon hematocrit sensing by thesensors, with the desired FF. The machine 16 issues a command to theflow restrictor to bring the difference to zero.

Waste fluid removal optimization can also be achieved by maintaining amaximum specified transmembrane pressure in the hemofilter bymanipulating blood flow rate, and/or venous blood pressure, and/or wastefluid pressure. This optimization technique can be undertaken once atthe outset of a given procedure, or at several intervals during thecourse of a procedure. In this arrangement, arterial blood pressuresensing (or derivation thereof based upon flow rate sensing) isimplemented to achieve a maximum blood flow rate. A fixed or variableflow restrictor is placed in the venous blood return path to maintain aset maximum transmembrane pressure (e.g., 600 mmHg) while the maximumarterial blood flow rate is maintained. Pressure is sensed in the venousblood return path to assure that venous pressure does not exceed a setmaximum amount (e.g., 250 mmHg), which is set for safety reasons. Wastefluid pressure is kept slightly above 50 mmHg. Together, control oftransmembrane pressure at the maximum blood flow rate and control ofwaste fluid pressure at a maximum blood flow rate, maximize the wastefluid removal rate.

5. Set Up Pressure Testing/Priming

Upon mounting the disposable fluid circuit 18 on the machine 16, thepumps can be operated in forward and reverse modes and the valvesoperated accordingly to establish predetermined pressure conditionswithin the circuit. The sensors monitor build up of pressure within thecircuit, as well as decrease in pressure over time. In this way, themachine can verify the function and integrity of pumps, the pressuresensors, the valves, and the flow paths overall.

The machine 16 can also verify the accuracy of the ultrafiltration pumpusing the fluid balancing containers.

Priming can be accomplished at the outset of each hemofiltration sessionto flush air and any residual fluid from the disposable fluid circuit.Fluid paths from the blood lines to the waste bag are flushed withreplacement fluid. Replacement fluid is also circulated through thefluid balancing containers into the waste bag and the venous returnpath. The higher flow rate in the replacement fluid path and timing ofthe fluid balancing valve elements assure that the replacement fluidcompartments completely fill and the waste fluid compartments completelyempty during each cycle for priming.

6. Rinse Back

As previously described, waste fluid pressure is controlled andmonitored to assure its value is always positive. Likewise, pressurebetween the blood pump and the hemofilter must also be positive, so thatair does not enter this region of the circuit. Forward operation of theblood pump to convey arterial blood into the hemofilter establishes thispositive pressure condition.

In this arrangement, no air sensing is required in the blood line, and apressure sensor between the blood pump and the hemofilter is required.

7. Using the GUI

When configured to guide an operator to perform hemofiltration, oranother treatment modality, the GUI 324 (see FIG. 19) can, e.g., includean array of icon-based touch button controls 326, 328, 330, and 332. Forexample, the controls can include an icon-based treatment start/selecttouch button 326, an icon-based treatment stop touch button 328, anicon-based audio alarm mute touch button 330, and an icon-based addfluid touch button 332.

An array of three numeric entry and display fields can appear betweenthe icon-based touch buttons. The fields can comprise informationdisplay bars 334, 336, and 338, each with associated touch keys 340 toincrementally change the displayed information.

The associated touch keys 340 can be provided to point up (to increasethe displayed value) or down (to decrease the displayed value), tointuitively indicate their function. The display bars 334, 336, and 338and touch keys 340 can be shaded in different colors.

An array of status indicator bars can appear across the top of thescreen. The left bar 342, when lighted, displays a safe color (e.g.,green) to indicate a safe operation condition. The middle bar 344, whenlighted, displays a cautionary color (e.g., yellow) to indicate acaution or warning condition and may, if desired, display a numeric orletter identifying the condition. The right bar 346, when lighted,displays an alarm color (e.g., red) to indicate a safety alarm conditionand may, if desired, display a numeric or letter identifying thecondition.

The display can also a processing status touch button 348. For example,the button 348, when touched, can change for a period of time (e.g., 5seconds) the values displayed in the information display bars 334, 336,and 338 , to show the corresponding current real time values, e.g., fora hemofiltration modality, the replacement fluid volumes exchanged (inthe top display bar 334), the ultrafiltrate volume (in the middledisplay bar 336), and the blood volume processed (in the bottom displaybar 338). The status button 348, when touched, can also show the elapsedprocedure time in the left status indicator bar 342.

The display can also include a cartridge status icon 350. The icon 350,when lighted, can indicate that the cartridge 18 can be installed orremoved from the machine 16.

In a preferred arrangement, the GUI 324 can employ a touch button inputverification function, which monitors the information provided by thetouch button controls. The input verification function inputs theinformation provided by a given touch button control both to the systemcontrol processor and to the system safety processor. The two processorscommunicate using an appropriate handshake protocol when the informationreceived by the system control processor matches the informationreceived by the system safety processor. The handshake allowsinformation input to proceed for execution. The lack of a handshakebetween the system control processor and system safety processorindicates a possible information input error. In this instance, the GUIgenerates an error signal which requires a re-entry of the informationinput and a subsequent handshake before information input can proceedfor execution.

As FIG. 19 shows, the interface can also include an infrared port 360 tosupport the telemetry function, as already described.

The GUI 324, though straightforward and simplified, enables the operatorto set these various processing parameters for a given hemofiltrationsession in different ways.

For example, in one input mode for hemofiltration, the GUI 324 canprompt the operator by back-lighting the replacement fluid display bar334, the ultrafiltration display bar 336, and the blood flow ratedisplay bar 338. The operator follows the lights and enters the desiredprocessing values using the associated touch up/down buttons 340. TheGUI back-lights the start/select touch button 326, prompting theoperator to begin the treatment. In this mode, the machine 16 controlsthe pumps to achieve the desired replacement fluid, ultrafiltration, andblood flow rates set by the operator. The machine terminates theprocedure when all the replacement fluid is used and the netultrafiltration goal is achieved.

In another input mode for hemofiltration, the operator can specifyindividual processing objectives, and the machine 16 will automaticallyset and maintain appropriate pump values to achieve these objectives.This mode can be activated, e.g., by pressing the start/select touchbutton 326 while powering on the machine 16. The GUI 324 changes thefunction of the display bars 334 and 336, so that the operator canselect and change processing parameters. In the illustrated embodiment,the processing parameters are assigned identification numbers, which canbe scrolled through and selected for display in the top bar 334 usingthe touch up/down keys 340. The current value for the selected parameteris displayed in the middle display bar 336, which the operator canchange using the touch up/down keys 340.

In this way, the operator can, e.g., specify a desired filtration factorvalue (FF) along with a desired ultrafiltration flow rate (UFR) andreplacement fluid flow rate (RFR). The machine will automaticallycontrol the blood pump rate (BFR), based upon the relationshipBFR=(RFR+UFR)/FF, as already described.

Alternatively, the operator can specify a desired filtration factorvalue (FF) along with a desired ultrafiltration flow rate (UFR) andblood flow rate (BFR). The machine will automatically control thereplacement fluid pump rate (RFR), based upon the relationshipRFR=(BFR*FF)−UFR, as already described.

Alternatively, the operator can specify only an ultrafiltration volume.In this arrangement, the machine 16 senses waste fluid pressure toautomatically control the blood flow rate to optimize the removal offluid across the hemofilter 34, as previously described. Alternatively,the machine can automatically control the blood flow rate to optimizeremoval of fluid based a set control arterial blood pressure, as alsoalready described. Still alternatively, the machine can automaticallyoptimize the ultrafiltration flow rate and blood flow rate to achievethe desired net ultrafiltration volume.

In another mode, the operator can specify both replacement fluid volumeand ultrafiltration volume to remove. In this arrangement, the machineperforms a countdown of the sum of the two fluid volumes to minimize theduration of the treatment.

While particular devices and methods have been described, once thisdescription is known, it will be apparent to those of ordinary skill inthe art that other embodiments and alternative steps are also possiblewithout departing from the spirit and scope of the invention. Moreover,it will be apparent that certain features of each embodiment can be usedin combination with devices illustrated in other embodiments.Accordingly, the above description should be construed as illustrative,and not in a limiting sense, the scope of the invention being defined bythe following claims.

1. A fluid balancing system comprising: first and second chambersalternately fed by an incoming fluid that is consumed by a process andan outgoing fluid that is discarded from said process; said first andsecond chambers being configured to displace fluid mutually such that asone is filled, fluid is forced out of the other and vice versa; anincoming fluid supply mechanism that conveys incoming fluid into saidfirst chamber during a first cycle such that said first chamber isentirely filled with said incoming fluid, thereby displacing saidoutgoing fluid from said second chamber; an outgoing fluid supplymechanism that conveys outgoing fluid into said second chamber during asecond cycle such that said second chamber is only partly filled withsaid outgoing fluid, thereby displacing an equal volume of said incomingfluid from said first chamber.
 2. A system as in claim 1, wherein saidoutgoing fluid supply includes a positive displacement pump that iscontrolled such that it displaces, during each of said first and secondcycles, no more fluid than required to partially fill a respective oneof said first and second chambers.
 3. A system as in claim 2, whereinsaid first and second cycles correspond to respective inlet and outletvalve configurations which control said incoming and outgoing fluidsupply mechanisms and said positive displacement pump is mechanicallysynchronized with a mechanical mechanism that controls said valveconfiguration.
 4. A system as in claim 3 wherein said incoming fluidsupply mechanism includes a pump mechanism and a fluid bypass configuredto allow said incoming fluid to recirculate once a respective one ofsaid first and second chambers is filled, said first cycle being suchthat said incoming fluid is supplied at such a volume that it completelyfills said respective one of said first and second chambers causing itto recirculate, whereby a complete filling of said respective one ofsaid first and second chambers is ensured.
 5. A system as in claim 1,wherein said incoming fluid supply mechanism includes a pump mechanismand a fluid bypass configured to allow said incoming fluid torecirculate once a respective one of said first and second chambers isfilled, said first cycle being such that said incoming fluid is suppliedat such a volume that it completely fills said respective one of saidfirst and second chambers causing it to recirculate, whereby a completefilling of said respective one of said first and second chambers isensured.
 6. A system as in claim 1, wherein said first and second cyclescorrespond to respective inlet and outlet valve configurations whichcontrol said incoming and outgoing fluid supply mechanisms and saidpositive displacement pump is mechanically synchronized with amechanical mechanism that controls said valve configuration.